1. Technical Field
The present invention relates to a lighting device and a projector.
2. Related Art
In recent years, an ultra-high pressure mercury lamp is often used as a light source for a projection image display device. However, because of problems such as a durable life of a lamp, impossibility of instant lighting, narrowness of a color reproducibility range, and light resistance of a liquid crystal light valve due to irradiation of light with an ultraviolet wavelength, a projector that uses a laser as a light source and lights a light modulator such as the liquid crystal light valve is proposed (see, for example, JP-A-11-64789 and JP-A-2000-162548).
A laser display device described in JP-A-11-64789 sets light emitted from laser light sources of three colors, red, green, and blue, in a uniform intensity distribution with an optical integrator. Then, the laser display device modulates light emitted from the optical integrator with a spatial light modulator to display an image. A projection display device described in JP-A-2000-162548 uses a white laser light source and separates a color of light into three colors, red, green, and blue, with a dichroic mirror. Thereafter, the projection display device spatially modulates, in respective reflection liquid crystal display panels, illumination lights in respective wavelength bands with video signals corresponding to the illumination lights to display an image.
When a predetermined optical system is used for lighting an incidence surface of a light modulator with a laser beam in a uniform illuminance distribution, depending on a structure of the optical system, it is likely that increase in size and complexity of the device or increase in cost of the device is caused. Further, depending on a structure of the optical system, it is likely that fall in light use efficiency or the like is caused. Thus, when a diffractive optical element is used as means for lighting the incidence surface in the uniform illuminance distribution, 0-th order light is generated because of a process error at the time of creation of the diffractive optical element or an error between a light source wavelength and that at the time of design (an error caused by a temperature change or the like) and a marked luminescent spot is caused in the light modulator.